In recent years, the total number of pixels in an imaging element included in a digital still camera and a digital video camera has been increasing rapidly, and the resolution of captured images has been improved. However, the large number of pixels reduces the light reception amount per pixel, with the result that noise in the captured images has increased.
The extension of exposure time is effective for suppressing the noise. However, when the exposure time is longer, camera shake blur and motion blur are easier to take place and the quality of the capture images is reduced.
Therefore, a technique has been proposed for removing camera shake blur and motion blur from a captured image with reduced quality (refer to Patent Literature 1 and Non Patent Literature 1). In the methods according to Patent Literature 1 and Non Patent Literature 1, an image in which camera shake blur and motion blur are removed is generated by performing a restoration process on a captured image using a Point Spread Function (PSF).
PSF is a function which shows the states of camera shake blur, motion blur, and out-of-focus blur. It should be noted that hereafter, the camera shake blur and motion blur are collectively referred to as blur.
Moreover, there is a case where a distance of the captured image is estimated using PSF. For example, there is a technique called Depth from Defocus (DFD) in which a distance is measured based on PSF which changes depending on the distance. More specifically, for example, the PSF of the defocus image is estimated using two images of all-in-focus image which is in focus and a defocus image in which is out of focus, and a distance is estimated by comparison between the estimated PSF and the PSF that is previously measured for each distance to the object.
The PSF used for image restoration and distance estimation is often estimated using a captured image which is transformed into a frequency range by Discrete Fourier Transform (DFT). In the case of DFD, an all-in-focus image which is in focus and a defocus image are obtained. The defocus image matches an image obtained by convoluting the PSF into the all-in-focus image. In other words, each of the frequency components for the defocus image matches the product of each of the frequency components for the all-in-focus image and each of the components for the PSF. Therefore, each of the frequency components for the PSF, for example, can be obtained by dividing each of the frequency components for the all-in-focus image by each of the frequency components for the defocus image.